Aluminum alloy for die casting and method of manufacturing cast aluminum alloy using the same

ABSTRACT

Disclosed are an aluminum alloy for die casting that has excellent thermal conductivity and corrosion resistance, which can be used for parts requiring heat dissipation and high corrosion resistance, and a method of producing a cast aluminum alloy using the same. 
     Provided is an aluminum alloy for die casting that may include an amount of about 8.5 to 10.5 wt % of silicon (Si); an amount of about 3.6 to 5.5 wt % of magnesium (Mg); an amount of about 0.3 to 1.0 wt % of iron (Fe); an amount of about 0.1 to 1.0 wt % of manganese (Mn); and the balance of aluminum (Al) and inevitable impurities, all the wt % are based on the total weight of the aluminum alloy.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Korean PatentApplication No. 10-2019-0167378, filed on Dec. 16, 2019, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to an aluminum alloy for die casting and amethod of producing a cast aluminum alloy using the same. The aluminumalloy for die casting may have excellent thermal conductivity andcorrosion resistance, and may thus be used for parts requiring heatdissipation and high corrosion resistance.

BACKGROUND

In general, aluminum (Al) has been widely used throughout variousindustries because it is easy to cast, alloys well with other metals,has excellent corrosion resistance in an ambient atmosphere, andexhibits superior electrical and thermal conductivity.

In particular, in recent years, aluminum has been actively used toreduce the weight of vehicles and improve fuel efficiency, and aluminumalloys, obtained by mixing aluminum with other metals, have beencommonly used because aluminum itself is not as strong as other metals.

Die casting has been widely used as a method of manufacturing a productusing such an aluminum alloy. Die casting is a precision casting methodthat involves injecting a molten metal into a mold having a cavityprecisely machined to have a desired shape to obtain a cast producthaving the same shape as the cavity.

For the die casting to produce the molded alloy product, aluminum alloysmay need properties that meet the requirements of methods includingfilling the cavity in the die with a molten metal at a high rate andunder high pressure, followed by solidification. For example, aluminumalloys for die casting should have a fluidity suitable for high-pressurecasting and compensate for shrinkage defects that may occur duringsolidification by providing appropriate levels of high-temperatureviscosity and latent heat.

Currently widely used aluminum alloys for die casting includeAl—Si-based alloys such as ADC 3, ADC 10 and ADC 12 and Al—Mg-basedalloys such as ADC 5 and ADC 6. However, these aluminum alloys for diecasting have a limitation on widening the application range due to thelow heat dissipation and corrosion resistance thereof.

In the related field, aluminum alloys for die casting capable ofimproving thermal conductivity and corrosion resistance have beenreported.

However, although thermal conductivity and corrosion resistance may beimproved to some extent, there has been limitation in effectiveness inimproving the thermal conductivity and corrosion resistance due to thelow ratio of Mg content to Si content in conventional aluminum alloys.

The above information disclosed in this Background section is providedonly for enhancement of understanding of the background of the inventionand therefore it may contain information that does not form the priorart that is already known in this country to a person of ordinary skillin the art.

SUMMARY

In preferred aspects, provided are an aluminum alloy for die castingwhich has excellent thermal conductivity and corrosion resistance, amolded product, such as parts or vehicle parts requiring heatdissipation and high corrosion resistance and a method of producing acast aluminum alloy using the same. Particularly, the aluminum alloy maybe obtained by controlling the contents of Si, Mg, Fe and Mn, containedalong with Al,

In an aspect, provided is an aluminum alloy for die casting which canmaintain superior castability and formability while maintainingexcellent thermal conductivity and corrosion resistance, by controllingthe contents of Si and Mg and the ratio therebetween. In another aspect,provided is a method of producing a cast aluminum alloy using the same.

An aluminum alloy for die casting may include an amount of about 7.8 to10.5 wt % of silicon (Si); an amount of about 3.6 to 5.5 wt % ofmagnesium (Mg); an amount of about 0.3 to 1.0 wt % of iron (Fe); anamount of about 0.1 to 1.0 wt % of manganese (Mn); and a balance ofaluminum (Al) and other inevitable impurities. All the wt % are based onthe total weight of the aluminum alloy.

The aluminum alloy may further include an amount of about 0.002 to 0.02wt % of beryllium (Be).

Preferably, the aluminum alloy may include the silicon (Si) in an amountof about 8.0 to 10.5 wt %.

A ratio of Si/Mg may be not less than about 1.5 and less than about 3.0.

A total content of copper (Cu), zinc (Zn) and nickel (Ni) contained asimpurities in the aluminum alloy may be in an amount of about 0.2 wt %or less.

The aluminum alloy may have a yield strength of about 260 MPa orgreater.

The aluminum alloy may have a tensile strength of about 320 MPa orgreater.

The aluminum alloy may have an elongation of about 2.0 to 3.0%.

The aluminum alloy may have a thermal conductivity of about 135 w/m·K orgreater.

The aluminum alloy may have an electrical conductivity of about 30% IACSor greater.

Further provided is a method of producing a cast aluminum alloy. Themethod may include: preparing a molten aluminum (Al) batch by meltingaluminum (Al) or an Al scrap; preparing heating the prepared molten Albatch; preparing a primary molten alloy by adjusting a content ofsilicon (Si) in the heated molten Al to about 7.8 to 10.5 wt % therebyconducting a primary alloying; secondary heating the primary moltenalloy; preparing a secondary molten alloy by adjusting a content of iron(Fe) in the heated primary molten alloy to about 0.3 to 1.0 wt % andadjusting a content of manganese (Mn) to about 0.1 to 1.0 wt % therebyconducting a secondary alloying; cooling the secondary molten alloy; andpreparing a tertiary molten alloy by adjusting a content of magnesium(Mg) in the cooled secondary molten alloy to about 3.6 to 5.5 wt %thereby conducing a tertiary alloying. All wt % are based on the totalweight of the cast aluminum alloy.

The primary alloying may include adjusting the content of Si to about8.0 to 10.5 wt % to prepare a primary molten alloy.

The secondary alloying may include further adding an amount of about0.002 to 0.02 wt % of beryllium (Be) to the heated primary molten alloy.

The primary heating may include heating the molten Al batch to a firsttemperature of about 800 to 850° C.

The secondary heating may include heating the primary molten alloy to asecond temperature of about 900 to 950° C.

The cooling may include cooling the secondary molten alloy to a thirdtemperature of about 700 to 750° C.

The method may further include casting of injecting the tertiary moltenalloy into a mold to produce a cast aluminum alloy.

The casting may include injecting the tertiary molten alloy at a castingtemperature of about 680 to 750° C. into a mold for die casting.

Also provided is a molded product, for example, vehicle part, thatincludes the aluminum alloy as described herein. For example, the moldedpart may be manufactured by the methods described herein, using thealuminum alloy.

Other aspect of the invention are disclosed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 shows an image comparing the result of a saline spray testbetween Comparative Example 2 and Example 3 according to an exemplaryembodiment of the present invention;

FIG. 2 shows an image comparing the result of a saline spray testbetween Comparative Example 1 and Examples 1-2 according to an exemplaryembodiment of the present invention;

FIG. 3 is an image showing microstructures of Comparative Example andExample according to an exemplary embodiment of the present invention;and

FIG. 4 is an image showing microstructures of specimens of ComparativeExample and Example according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. However, the present invention is not limited to theembodiments, and may be implemented in various forms. The embodimentsare provided only to fully illustrate the present invention and tocompletely inform those having ordinary knowledge in the art of thescope of the present invention.

The terminology used herein is for the purpose of describing particularexemplary embodiments only and is not intended to be limiting of theinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Unless specifically stated or obvious from context, as used herein, theterm “about” is understood as within a range of normal tolerance in theart, for example within 2 standard deviations of the mean. “About” canbe understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%,0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear fromthe context, all numerical values provided herein are modified by theterm “about.”

In as aspect, an aluminum alloy for die casting may include an amount ofabout 7.8 to 10.5 wt % of silicon (Si); an amount of about 3.6 to 5.5 wt% of magnesium (Mg); an amount of about 0.3 to 1.0 wt % of iron (Fe); anamount of about 0.1 to 1.0 wt % of manganese (Mn); and the balance ofaluminum (Al) and inevitable impurities. All the wt % are based on thetotal weigh of the aluminum alloy. In addition, the aluminum alloy mayfurther include an amount of about 0.002 to 0.02 wt % of beryllium (Be).

In addition, the aluminum alloy for die casting may, optionally, notcontain copper (Cu), zinc (Zn) and nickel (Ni). However, the aluminumalloy may contain copper (Cu), zinc (Zn) and nickel (Ni) as inevitableimpurities. However, even when copper (Cu), zinc (Zn) and nickel (Ni)are contained as impurities, it is preferable to adjust the totalcontent thereof to about 0.2 wt % or less.

Next, the reason for limiting alloy ingredients and the compositionranges thereof will be described. All the wt % are based on the totalweight of the aluminum alloy (or its composition).

Silicon (Si) in an Amount of about 7.8 to 10.5 wt %

Silicon (Si) is a main element that may improve castability and abrasionresistance and affect thermal conductivity and strength.

When silicon (Si) is added in an amount less than about 7.8 wt %, theeffects of improving castability, abrasion resistance and strength areunsatisfactory, and when silicon (Si) is added in an amount greater thanabout 10.5 wt %, processability such as machinability of the obtainedcast product may be deteriorated and heat treatment may be ineffective.Thus, the content of silicon (Si) is limited to this range.

In particular, silicon (Si) is an essential element for securing thefluidity and formability of the molten metal during the die-castingprocess. Corrosion resistance may be improved as the content ofmagnesium (Mg) increases, whereas formability and fluidity areremarkably deteriorated as the content of magnesium (Mg) increases. Inorder to compensate for these problems, the temperature of the moltenmetal may be increased during die casting so as to obtain products.However, when the temperature of the molten metal increases,productivity may be lowered and the defect rate is increased. Forexample, hot cracking of products may occur and the lifetime of the moldfor die casting may be reduced.

In order to regulate this problem in the alloy, the Si content may beincreased. The Si content may be adjusted to about 7.8 to 10.5 wt % toensure corrosion resistance, castability and productivity. Preferably,the Si content may range from about 8.0 to about 10.5 wt %, orparticularly from about 8.5 to about 10.5 wt %.

Magnesium (Mg) in an Amount of about 3.6 to 5.5 wt %

Magnesium (Mg) is a main element which may improve not only corrosionresistance, but also strength and elongation, and processability ofcastings, when it becomes a sacrificial corrosion site due to the Mg₂Sicrystallized phase formed by reaction with silicon (Si).

When the magnesium (Mg) is present in an amount of less than about 3.6wt %, the effects of improving corrosion resistance, strength andelongation may be insignificant. When the magnesium (Mg) is present inan amount greater than about 5.5 wt %, the castability may be decreaseddue to reduced flowability of the molten metal during casting and thedross may be increased due to increased oxidation tendency of the moltenmetal. Thus, the content of magnesium (Mg) is limited to this range.

Iron (Fe) in an Amount of about 0.3 to 1.0 wt %

Iron (Fe) is an element that contributes to preventing mold burn-on andproduct scratching.

In this case, when iron (Fe) is present in an amount less than 0.3%, theeffect of improving strength is insignificant, and when iron (Fe) ispresent in an amount exceeding 1%, abrasion resistance and thermalconductivity are deteriorated. Thus, the content of iron (Fe) is limitedto this range.

Manganese (Mn) in an Amount of about 0.1 to 1.0 wt %

Manganese (Mn) is an element that may contribute to the reinforcement ofthe solid solution along with iron (Fe), thus improving thehigh-temperature strength of the casting, preventing mold burn-on andimproving solubility.

When the manganese (Mn) is present in an amount of less than about 0.1wt %, the effect of improving strength may be insignificant, and whenthe manganese (Mn) is present in an amount greater than about 1.0 wt %,castability and machinability may be decreased and thermal conductivitymay be reduced. Thus, the content of manganese (Mn) is limited to thisrange.

Beryllium (be) in an Amount of about 0.002 to 0.02 wt %

Beryllium (Be) is an element which may prevent the oxidation ofmagnesium (Mg), inhibit the formation of dross during casting, andimprove corrosion resistance.

When the beryllium (Be) is present in an amount of less than about 0.002wt %, the effect of improving corrosion resistance may be insignificant,and when the beryllium (Be) is present in an amount greater than about0.02 wt %, the corrosion resistance may be decreased. Thus, the contentof beryllium (Be) is limited to this range.

Meanwhile, other than the aforementioned ingredients, the balance iscomposed of aluminum (Al) and other inevitable impurities.

For example, in order to ensure corrosion resistance of the aluminumalloy to a desired level, the aluminum alloy preferably does notoptionally contain copper (Cu), zinc (Zn), or nickel (Ni), which areelements causing corrosion. However, even when copper (Cu), zinc (Zn)and/or nickel (Ni) are inevitably contained, it is preferable to adjustthe total content thereof to about 0.2 wt % or less.

In addition, the ratio of Si/Mg may be limited to not less than about1.5 and less than about 3.0, for properly generating Mg₂Si, which is afactor enhancing corrosion resistance. In addition, the Si content maybe adjusted in order to prevent a decrease in castability compared tothe improvement in abrasion resistance and strength, a decrease inproductivity due to the increased incidence of hot cracking, and anincrease in the defect rate, all of which are caused by the increased Mgcontent. The increase in thermal conductivity can be expected throughoptimization of the two ingredients.

When the ratio of Si/Mg is less than about 1.5, the Si content may berelatively less than the Mg content, which cause problems in thatcastability is lowered and hot cracking occurs during casting. Inaddition, when the ratio of Si/Mg is greater than about 3.0, therelative Si content may be increased and the Mg content is decreased,which causes problems in that the improvements in corrosion resistanceand strength do not reach desired levels. In an aspect, provided is amethod for producing a cast aluminum alloy. The case aluminum alloy mayinclude the composition of the aluminum alloy described herein.

First, aluminum (Al) or an Al scrap may be melted at a temperature ofabout 750° C. to prepare molten Al (preparing molten Al). High-qualityAl scrap may be preferably used n order to minimize the content ofimpurities contained in the Al scrap. For example, in order to reducethe content of Cu, which is an element lowering corrosion resistance, toabout 0.15 wt %, it is preferable to use only a wrought aluminumhigh-quality aluminum scrap as the Al scrap. Therefore, preferably,1000-, 6000-, and 7000-based Al scraps should not be used.

When molten Al is prepared by sufficiently melting Al or Al scrap, theprepared molten Al may be heated to a first temperature of about 800 to850° C. (primary heating).

When the molten Al is heated to the first temperature of 800 to 850° C.,the content of Si in the molten Al may be adjusted to about 8.5 to 10.5wt % to prepare a primary molten alloy in which Si is sufficientlymelted (primary alloying).

When the primary molten alloy having a controlled Si content in Al isprepared as described above, the primary molten alloy may be heated to asecond temperature of about 900 to 950° C. (secondary heating).

Then, the content of Fe in the heated primary molten alloy may beadjusted to about 0.3 to 1.0 wt % and the content of Mn may be adjustedto about 0.1 to 1.0 wt % to prepare a secondary molten alloy (secondaryalloying).

The content of Be in the heated primary molten alloy may be adjusted toabout 0.002 to 0.02 wt %.

In order to sufficiently melt Fe, Mn and Be in the primary molten alloy,the elevated temperature may sufficiently be maintained for about 5hours.

Thus, when the secondary molten alloy is prepared, the secondary moltenalloy may be cooled to a third temperature of about 700 to 750° C.(cooling).

Then, the content of Mg in the cooled secondary molten alloy may beadjusted to about 3.6 to 5.5 wt % to prepare a tertiary molten alloy(tertiary alloying).

Meanwhile, the temperature ranges presented in the primary heating, thesecondary heating and the cooling may be designed to control aluminum(Al) oxide and magnesium (Mg) oxide, and unnecessary aluminum (Al) oxideand magnesium (Mg) oxide may be produced out of the temperature rangesuggested in each step, which impedes homogeneous alloying, so thedesired physical properties cannot be achieved in the present invention.

For example, when the temperature maintained during the cooling is lessthan the suggested third temperature, magnesium carbonate may begenerated during the tertiary alloying, causing the aluminum alloy tohave an undesirable yellow color. In addition, when the temperaturemaintained in the cooling is greater than the suggested thirdtemperature, magnesium oxide may be generated during the tertiaryalloying, causing the aluminum alloy to have an unwanted blue color.

At this time, cooling may be slowly conducted while maintaining thetemperature of the tertiary molten alloy at the temperature of about 700to 750° C. for about 1 hour. Thus, dross and oxides produced in thetertiary molten alloy may be removed.

The adjusting the content of each alloyed element during the primary totertiary alloying described above may include adjusting the content ofeach alloyed element contained in the molten alloy to the desired range.Accordingly, in the case of preparing the molten Al using pure Al in thepreparation of molten Al, the content of each alloyed element duringeach alloying step may be adjusted by adding the element in the contentto be adjusted. On the other hand, in the case of preparing molten Alusing an Al scrap in the preparation of molten Al, the other alloyedelements may already be contained in the molten Al as impurities, beforethe addition of each alloyed element during each alloying. As such, thecontent of each alloyed element can be adjusted by measuring the contentof the corresponding element and then adding the corresponding elementin an amount corresponding to the difference from the content to beadjusted.

When the tertiary molten alloy is prepared, the tertiary molten alloymay be injected into a mold to produce a cast aluminum alloy product(casting).

The casting may be carried out by injecting the tertiary molten alloyinto a mold for die casting while maintaining the tertiary molten alloyat a casting temperature of about 680 to 750° C. in order to ensuresmooth casting.

The casting may be a step of casting a final product by injection intothe mold for die casting, but the casting is not limited to the step ofcasting the final product, and may be a step of casting an ingot orintermediate product prepared to produce the final product.

According to the present invention, oxidation of the Mg component may beprevented as much as possible by adjusting the timing of addition of Mg,adjusting the temperature and retention time during the alloying, andadjusting the addition of Be and the timing of addition thereof.

Example

Hereinafter, the present invention is described with reference toExamples and Comparative Examples.

Various compositions of Examples according exemplary embodiments of thepresent invention and Comparative Examples are shown in Table 1 below,and the specimens according to Examples and Comparative Examples areproduced as ASTM sub-size specimens by heating the tertiary molten alloyprepared according to the method for producing a cast aluminum alloy asdescribed above to a temperature of 680 to 750° C. and by injecting thesame into an ASTM sub-size plate mold at 75 MPa.

TABLE 1 Item Al Si Mg Fe Mn Be Cu Zn Ni Sn Pb Ti Si/Mg Example 1 Balance8.5 3.6 0.3 0.1 — — — — — — — 2.4 Example 2 Balance 9.0 4.5 0.5 0.30.005 — — — — — — 2.0 Example 3 Balance 9.5 5.5 0.6 0.5 0.007 — — — — —— 1.7 Comparative Balance 7.5 2.5 0.5 0.1 — — — — — — — 3.0 Example 1Comparative Balance 12 0.2 0.8 0.1 — 3.0 0.7 0.3 0.1 0.1 0.1 60.0Example 2

Comparative Example 1 is an alloy composition in the related art, andComparative Example 2 is ALDC12, which is a conventional generalaluminum alloy for die casting and is a commercially availableAl—Si-based alloy.

In addition, the produced specimens were tested to measure thermalconductivity, electrical conductivity, tensile strength, yield strengthand elongation, and the results are shown in Table 2 below.

Thermal conductivity and electrical conductivity were measured afterprocessing the prepared specimens into specimens 10 mm*10 mm*2t in size.At this time, the thermal conductivity was measured according to thethermal conductivity measurement test (ASTM E 1461).

In addition, the tensile strength and yield strength were measuredaccording to the tensile test (KS B 0802).

In addition, the saline spray test was carried out, and the results areshown in FIGS. 1 and 2.

The saline spray test was carried out according to the saline spray test(KS D 9502) using 5% NaCl as saline after preparing the prepared ASTMsubsize die-casting tensile test specimen.

TABLE 2 Thermal Electrical Tensile Yield conductivity conductivitystrength strength Elongation Item (W/m · K) (% IACS) (MPa) (MPa) (%)Example 1 150 33 347 260 3.0 Example 2 144 32 332 277 2.6 Example 3 14030 323 291 2.0 Comparative 140 30 320 260 4.0 Example 1 Comparative  9627 300 150 3.0 Example 2

As shown in Table 2, exemplary cast aluminum alloys had excellentphysical properties, for example, the thermal conductivity thereof was135 W/m·K or greater, the electrical conductivity thereof was 30% IACSor greater, the tensile strength thereof was 320 MPa or greater, theyield strength thereof was 260 MPa or greater and elongation thereof was2.0 to 3.0% or greater.

In particular, when compared with Comparative Example 2, which is aconventional general aluminum alloy for die casting, the yield strengthof the exemplary aluminum alloy was improved by about 70% or greater,the thermal conductivity was improved by 40% or greater, and theelongation can be secured at an equivalent level or higher. Thus, thecast products in exemplary embodiments of the present invention havingsubstantially improved properties compared to those of conventional castproducts were produced. Thus, the aluminum alloy for die castingaccording to exemplary embodiment of the present invention can be usedfor electronic parts for vehicles and portable electronic devices.

In addition, FIG. 1 is an image comparing Example 3 according to anexemplary embodiment of the present invention with Comparative Example2, 24 hours and 48 hours after saline (NaCl 5%) spraying, and FIG. 2 isan image comparing Example 3 according to an exemplary embodiment of thepresent invention with Comparative Example 2, in an initial stage, onthe first day and the second day after spraying saline (NaCl 5%).

As shown in FIG. 1, in Comparative Example 2 (ALDC12), which is one ofthe commercial Al—Si-based alloys, corrosion progressed seriously 24hours after the saline spraying, whereas Example 3 according to thepresent invention was able to maintain an initial state, in which littlecorrosion occurred, even after 48 hours.

In addition, as shown in FIG. 2, Comparative Example 1 showed partialcorrosion from the first day and Comparative Example 2 showed corrosionover the entire area thereof from the first day, whereas Examples 1 and2 according to exemplary embodiments of the present invention were ableto maintain an initial state, in which little corrosion occurred even onthe second day.

An experiment was also performed in order to determine whether or notMg₂Si microstructures were formed according to the variation in Mgcontent.

FIG. 3 is an image showing microstructures of Comparative Example andExample according to the present invention.

In order to determine the formation of Mg₂Si microstructures dependingon the variation in the content of Mg, an aluminum alloy containing anamount of 8.5 wt % of Si, an amount of 0.5 wt % of Fe, an amount of 0.1wt % of Mn, and the balance of Al and other inevitable impurities wasprepared as the wt % was based on the total weight of the aluminumalloy. The aluminum alloy was prepared by changing the contents of Mg to1.5 wt %, 3.0 wt % and 4.5 wt %, respectively, and then themicrostructure of the specimen prepared according to an exemplary methodof producing an aluminum alloy using the aluminum alloy was observed.

As shown in FIG. 3, microstructures of Mg₂Si, which is a factorenhancing corrosion resistance, were not observed in the specimencontaining 1.5 wt % of Mg. In addition, the Mg₂Si microstructures beganto be generated in the specimen containing 3.0 wt % of Mg, and aconsiderable amount of Mg₂Si microstructure was produced in the specimencontaining 4.5 wt % of Mg.

Additional experiment was conducted to determine the effect of improvingthe corrosion resistance depending on the variation in the content ofMg.

FIG. 4 is an image showing microstructures of specimens of ComparativeExample and Example according to the present invention.

In order to determine the effect of improving the corrosion resistanceaccording to the variation in Mg content, an aluminum alloy containingan amount of 8.5 wt % of Si, an amount of 0.5 wt % of Fe, an amount of0.1 wt % of Mn, and the balance of Al and inevitable impurities wasprepared as the Mg content was changed to 3.0 wt % and 4.5 wt %,respectively, a saline spray test was performed on the specimen preparedaccording to an exemplary method of producing an aluminum alloy usingthe aluminum alloy, and the results are shown in FIG. 4.

The saline spray test was carried out according to the saline spray test(KS D 9502) using 5% NaCl as saline after obtaining a prepared ASTMsub-size die casting tensile test specimen. At this time, theobservation was separately conducted at 0 hour, 48 hours and 96 hours.

As shown in FIG. 4, the specimen having a Mg content of 3.0 wt % hadrelatively good corrosion resistance, but, as can be seen from FIG. 4,compared to the 0-hr specimen, corrosion gradually occurred on thesurface of the 48-hr and 96-hr specimens over time.

On the other hand, the specimen having a Mg content of 4.5 wt % had veryexcellent corrosion resistance. In particular, when compared with the0-hr specimen, the 48-hr and 96-hr specimens had no corrosion on thesurface of the specimen even after the passage of time.

These results demonstrate a significant difference in corrosionresistance depending on the amount of the Mg₂Si microstructure.

The exemplary embodiments of the present invention have effects ofensuring excellent thermal conductivity and corrosion resistancecompared to conventional aluminum alloys for die casting, therebyenabling the production of a variety of cast products used in themanufacture of electronic parts for vehicles and portable electronicdevices, which require heat dissipation and high corrosion resistance.

In addition, the exemplary embodiments of the present invention have aneffect of producing cast products having excellent strength andelongation compared to conventional aluminum alloys for die casting.

Although the various exemplary embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. An aluminum alloy for die casting comprising: anamount of about 7.8 to 10.5 wt % of silicon (Si); an amount of about 3.6to 5.5 wt % of magnesium (Mg); an amount of about 0.3 to 1.0 wt % ofiron (Fe); an amount of about 0.1 to 1.0 wt % of manganese (Mn); and abalance of aluminum (Al) and other inevitable impurities, all wt % arebased on the total weight of the aluminum alloy.
 2. The aluminum alloyaccording to claim 1, further comprising an amount of about 0.002 to0.02 wt % of beryllium (Be).
 3. The aluminum alloy according to claim 1,wherein the aluminum alloy comprises an amount of about 8.0 to 10.5 wt %of the silicon (Si).
 4. The aluminum alloy according to claim 1, whereina ratio of Si/Mg is not less than about 1.5 and less than 3.0.
 5. Thealuminum alloy according to claim 1, wherein a total content of copper(Cu), zinc (Zn) and nickel (Ni) contained as impurities in the aluminumalloy is about 0.2 wt % or less.
 6. The aluminum alloy according toclaim 1, wherein the aluminum alloy has a yield strength of about 260MPa or greater.
 7. The aluminum alloy according to claim 1, wherein thealuminum alloy has a tensile strength of about 320 MPa or greater. 8.The aluminum alloy according to claim 1, wherein the aluminum alloy hasan elongation of about 2.0 to 3.0%.
 9. The aluminum alloy according toclaim 1, wherein the aluminum alloy has a thermal conductivity of about135 w/m·K or greater.
 10. The aluminum alloy according to claim 1,wherein the aluminum alloy has an electrical conductivity of about 30%IACS or greater.
 11. A method of producing a cast aluminum alloycomprising: preparing a molten aluminum (Al) batch by melting aluminum(Al) or an Al scrap to prepare molten Al; primary heating the preparedmolten Al batch; preparing a primary molten alloy by adjusting a contentof Si in the heated molten Al batch to about 7.8 to 10.5 wt % therebyconducting a primary alloying; secondary heating the primary moltenalloy; preparing a secondary molten alloy by adjusting a content of iron(Fe) in the heated primary molten alloy to about 0.3 to 1.0 wt % andadjusting a content of manganese (Mn) therein to about 0.1 to 1.0 wt %thereby conducting a secondary alloying; cooling the secondary moltenalloy; and preparing a tertiary molten alloy by adjusting a content ofmagnesium (Mg) in the cooled secondary molten alloy to about 3.6 to 5.5wt % thereby conducting a tertiary alloying, all the wt % based on thetotal weight of the case aluminum alloy.
 12. The method according toclaim 11, wherein the primary alloying comprises adjusting the contentof Si to about 8.0 to 10.5 wt % to prepare the primary molten alloy. 13.The method according to claim 11, wherein the secondary alloyingcomprises further adding a content of about 0.002 to 0.02 wt % ofberyllium (Be) to the heated primary molten alloy.
 14. The methodaccording to claim 11, wherein the primary heating comprises heating themolten Al batch to a first heating temperature of about 800 to 850° C.,the secondary heating comprises heating the primary molten alloy to asecond temperature of about 900 to 950° C., and the cooling comprisescooling the secondary molten alloy to a third temperature of about 700to 750° C.
 15. The method according to claim 11, further comprisingcasting of injecting the tertiary molten alloy into a mold to produce acast aluminum alloy.
 16. The method according to claim 15, wherein thecasting comprises injecting the tertiary molten alloy at a castingtemperature of about 680 to 750° C. into a mold for die casting.
 17. Avehicle part comprising an aluminum alloy of claim 1.